Thermionic valve circuits



Jan. 2, 1940. E. L. c. WHITE 2,185,363

THERMIONIC VALVE CIRCUITS TIME POTE NTI AL INVENTOR EL. C. WHITE TIME AT TOR/VE) Patented Jan. 2, 1940 'rnnamomc VALVE cmourrs Eric LawrenceCasling White, Hillingdon, lingland, assignor to Electric & MusicalIndustries Limited, Hayes, Middlesex, England, a company of GreatBritain Application December 8, 1937, Serial No. 178,640 In GreatBritain December 12, 1936 6 Claims.

This invention relates to thermionic valve circuits such as are employedin oscillation generators or the relaxation oscillator type which arefrequently employed for the purpose of generat- 6 ing saw-tooth voltagewaves or oscillators of the multivibrator type which may be employed forfrequency division or frequency multiplication or for counting purposes.

In the usual type of multivibrator circuit, two

10 thermionic valves are provided, the anode of one valve being coupledto the grid of the other and the anode of the latter valve being coupledto the grid of the first valve. The valves are arranged in such a mannerthat one valve inbeu coming conducting renders the previously conductingvalve non-conducting.

These circuits may be employed for discharging periodically a condenserwhich is connected between the anode and cathode of the first valve, thecondenser being charged in a manner dependent upon the particular use ofthe circuit. When employed for the purpose of generating voltages ofsaw-tooth wave form, the condenser is usually charged substantiallycontinuously through an impedance connected to a suitable source ofcurrent or through a diode or other suitable means, and when employedfor frequency division or for counting purposes the condenser is chargedin steps under the control of applied pulses.

It is the chief object of the present invention to provide a new orimproved circuit suitable for use for the above and other purposes.

According to the invention a thermionic valve circuit comprising acondenser having one plate connected to a point of substantially fixedpotential and adapted to be charged or discharged at a desiredratethrough a suitable device, so that the potential relative to groundof the other plate rises at said desired rate, to some value at which itis caused to be respectively discharged or charged through thegrid-cathode space of a valve to the grid of which the said other plateis connected, the said valve interacting with a further valve .toproduce sudden transitions of the cathode potential of said valvebetween predetermined upper and lower limits, whereby the charge. on hecondenser is rapidly restored to I its initial value and then thecircuit restored to w the condition in which the condenser may becharged or discharged at the desired rate.

In carrying out the invention, the thermionic valve circuit which isadapted to discharge or to charge a condenser arranged to berespectively 55 charged or discharged either through an impedance' or insteps under the control of applied pulses, comprises two valves, theanode of one of which is coupled to the control grid of the other andthrough a resistance or inductance to a source of anode current of whichthe negative end is earthed, whilst the cathode of the one valve isconnected directly to the cathode of the other and through a resistanceor inductance to earth, and the condenser, which is adapted to bedischarged or charged, is connected between 10 the control grid of thefirst-mentioned valve and a point of fixed potential such as earth, oralternatively the high voltage line. the arrangement being such that thevalves interact so that when one valve is conducting the other is renl5dered non-conducting.

The valves are chosen and arranged so that the second passes aconsiderably greater current than the first. The potential of thecathodes thus undergoes transitions between two limits according towhich or the valves is conducting and passing its current through theresistance in the common lead of said cathodes. With such an arrangementthe condenser is discharged or charged as soon as grid current flows inthe grid circuit of the associated valve, i. e., as soon as the cathodepotential falls below the grid potential of said valve. The couplingbetween the anode of the one valve and the grid of the other valve ispreferably of the resistance-capacity typ a leak resistance beingprovided between the grid and cathode of the second-mentioned valve. Theparticular disposition and manner of charging or discharging of thecondenser depends upon the type of circuit to which the invention isapplied.

In order that the said invention may be clearly understood and readilycarried into effect it will now be described in detail with reference tothe accompanying drawing in which- Fig. l is a diagram of a circuitconstructed in accordance with the preferred form of the invention,

Fig. 2 is a diagram of a modification of a part of the circuit shown inFig. 1,

Fig. 3 is a further modification of part of the circuit shown in Fig; 1and Figs. 4 and 5 are explanatory diagrams. Referring to Fig. 1 thecircuit comprises twovalves l and 2, which, in the example shown,

are of the triode type, the anode of the first valve being connectedthrough a resistance 3 to the positive terminal of an associated sourceof anode current indicated by a battery 4, the anode also beingconnected through a coupling condenser 5 to the control grid of thevalve 2. The anode of the valve 2 is directly connected to the positiveterminal of the source of anode current whilst the two cathodes of thevalves are directly connected together, a resistance Ii being providedbetween the point of connection of the two cathodes and earth, as shown.A leak resistance I is provided between the control grid of the valve 2and the cathodes of the valves. The condenser, which is arranged to berapidly discharged through the grid circuit of valve I, is indicated at8, and is connected in the grid circuit of valve I between the controlgrid and earth.

In the example shown, the condenser 8 is arranged to be charged at adesired rate through a resistance 8, one end of which is connected tothe condenser 8, whilst the other end is connected to the positiveterminal of the source of anode current 4. During operation of thecircuit, the condenser 8 is slowly charged through the resistance 9 andis suddenly discharged, as hereinafter more particularly referred to,producing a voltage of saw-tooth wave form. Instead of charging thecondenser 8 through the resistance 9, it may be charged through someother high impedance, such as a saturated diode for producing a morelinear saw-tooth wave or a choke coil. The time constant of thecondenser 8 and the charging device controls the form of the risingvoltage across the condenser 8, whilst the duration of the chargingperiod of the condenser 8, that is to say of the slow rising portion ofthe saw-tooth wave, depends on the potential to which the cathode of thevalve I is raised by the anode current of the valve 2 flowing throughthe resistance 6.

The operation of the circuit will now be described with reference toFig. 4.

The line G represents the saw-tooth potential appearing on the grid I8of valve I to which the condenser 8 is connected. This represents thevoltage across the condenser 8, that is between grid I8 and earth. Thedotted line C represents the corresponding variation of potential of thecathode II of the valve I, and it will be seen that this makes suddentransitions between limits V1 and V2 corresponding to the respectivepotential drops across resistance 6 due to the anode current of eithervalve I or valve 2. A cycle of operations occurs as follows starting atthe point 2| in Fig. 4.

At this point the condenser 8 has been discharged down to voltage V1 in,a manner to be described. Valve 2 has just become conducting and so thecathode II of valve I is at a potential V: such that valve I iseffectively biased well beyond anode current cut-off. The condenser 8 isthen charged up through resistance 9 by the high voltage source 4, asshown by the line 2I22-23. As the potential of grid I8 rises up towardsthat of the cathode II the effective grid bias of the valve I becomesless negative until at some point such as 22 the valve I starts to passa little anode current. This results in a fall of potential of the anodeI2 which is instantaneously applied via condenser 5 to the grid I3 01'valve 2, resulting in a decrease of anode current through valve 2 andresistor 6 whereby the potential of cathode II falls thus increasing theanode current of valve I and further lowering the potential of its anodeI 2. The two valves thus react on each other by this cumulative processuntil the anode current of valve 2 decreases substantially to zero andthe potential of cathode II falls to the value V1 corresponding to thepassage through resistor 8 of the anode current of valve I only. It willtherefore be seen that the potential of cathode I I undergoes a rapidtransition from the value V2 to the value V1, as indicated in Fig. 4 bythe line 282324. The potential of grid I8 continues to rise for a shortdistance beyond the point 22 until it becomes equal to the fallingcathode potential at point 23; thereafter the grid tends to be positivewith respect to the cathode, so that grid current flows and allows thecondenser 8 to be rapidly discharged through the comparatively lowresistance of the now conducting grid-cathode space and the resistance8. In fact, the grid I8 follows the cathodedown to the potential V1 andthe condenser is discharged down to V1 as indicated by the line 23-24.However, the nonconducting condition of valve 2 due to the sudden fallof its grid potential is not a stable one, since the condenser 5 chargesup through grid-leak resistance 1 and the anode-cathode space of valve I(which is now conducting). The potential of grid I3 therefore startsrising again and valve 2 starts to conduct again, passing currentthrough resistance 8 which raises the potential of cathode II, decreasesthe. anode current of valve I and causes its anode I2 to rise inpotential. This potential rise is instantaneously communicated overcondenser 5 to grid I3 of valve 2 causing a further increase of anodecurrent of the said valve 2, which further raises the potential ofcathode I I, and so on. This cumulative process causes a second rapidtransition back to the original condition in which valve 2 isconducting, and valve I is biased back well beyond anode-current cut-offby the rise of potential of cathode II up to the value V2. The aboverise of potential of cathode II is indicated in Fig. 4 by the portion24--2| of line C and it will be seen that grid-current ceases at thepoint 24 and the condenser 8 starts charging up once more throughresistance 8 as indicated, by the part 2425 of line G.

The cycle of operations just described is automatically repeated so thata train of saw-tooth oscillations of potential appears across condenser8, between grid I8 and earth.

Figures 2 and 3, as stated above, show a modification of a part of thecircuit shown in Figure 1. That part of the circuit shown in Figure l tobe found at the left of the broken line may be replaced by Figure 2 orFigure 3, the four conductors shown at the right-hand portion of each ofthe figures being connected to the four conductors intersected by thebroken line shown in Figure 1.

Referring now to Fig. 2, a further example of the invention isillustrated in which the condenser 8 is connected across resistance 9,:Ietween the grid I8 of valve I and the high potential end of the source4, shown in Figure 1. Apart from this modification the circuit is thesame as in Fig. 1. In this case the saw-tooth voltage of Fig. 4 appearsbetween grid I8 and earthas before, while valves I and 2 interact in thesame way and the potential of cathode II varies in the same way as shownin Fig. 4. The operation differs from that of Fig. 1, however, in thatthe condenser 8 is now discharged slowly through resistance 9 during theperiod that valve I is nonconducting untilthe grid I8 rises to thepotential indicated by point 22 in Fig. 4, when the cathode II issuddenly lowered in potential as previously described and condenser 8 israpidly charged up again by the source 4 through the temporarily 75a1as,sas

conducting grid circuit of valve I. In this case it will be seen thatthe potential of grid 10 falls as the condenser it charges and viceversa, in contradistinction to the previous case Fig. 1. The condenser 8will in this case (Fig. 2) have across it a saw-tooth voltage which iscomplementary to curve G in Fig. 4;this is indicated at G in Fig. 5.

It will be seen, however, that the circuits of Figs. 1 and 2 have thecommon features that one plate of the condenser is connected to a pointof fixed potential while the other plate has a sawtooth variation ofpotential. It will be appreciated that the return stroke of thesaw-tooth oscillation (23-44 in Fig. 4) will be very fast due to thetrigger action of the circuit in lowering the potential of cathode I i.

According to a further feature of the invention for valve I there ischosen a multigrid valve such as a tetrode or pentode and one of thegrids such as a screening grid is adapted to serve the purpose of theanode l2 of Fig. 1 or Fig. 2, while the required output wave form istaken from the anode proper which is connected to the source or anodecurrent through some convenient impedance. This is illustrated in Fig.3, in which the elements are numbered to correspond with those of Fig.1.

The valve i is shown as a pentode and its screen grid M takes the placeof the anode I! of Fig. 1, while an impedance i6 is connected in thecircuit of the anode i5, from which the output potentials are taken.

For example impedance It may consist of a resistance and condenser inparallel, adjustment of which controls the amplitude of saw-toothpotentials taken from anode l5.

Where the invention is used forcounting or similar purposes it may bedesirable to stabilize the point at which the grid potential of valve Iis suddenly reduced by returning the grid-leak I in Fig. 1 to a point offixed potential, such as a tapping on a potentiometer associated withthe high voltage source 4.

Where the circuit is arranged for the purpose of counting pulses or forfrequency division or multiplication, controlling pulses may be appliedat a suitable point in the circuit and either in the positive ornegative sense according to the particular point of application of thepulses.

I claim:

1. A circuit for producing current and voltage variations of saw-toothwave form comprising a first and a second discharge device eachincluding at least a cathode, a control electrode and an anode, meansincluding a common resistance for connecting said cathodes to thenegative terminal of a source of potential, resistance means forconnecting the control electrode of said second device to said cathodes,means including a condenser for connecting the anode of said firstdevice to the control electrode of said second device, means forconnecting the anode of said second device to said source of potential,means including a resistance for connecting the anode of said firstdevice to said source of potential, a condenser and a resistanceconnected in series across the source of potential, and means forconnecting the control electrode of said first device to the junction ofsaid last named resistance and condenser.

2. A circuit for producing current and voltage variations of saw-toothwave form comprising a first and a second discharge device eachincluding at least a cathode, a control electrode and an anode, meansincluding a single resistance for connecting said cathodes to thenegative terminal of a source of potential, resistance means forconnecting the control electrode of said second device to said cathodemeans including a condenser for connecting the anode of said firstdevice to the control electrode of said second device, means forconnecting the anode of said second device to the positive terminal ofsaid source of potential, means including a resistance for connectingthe anode of said first device to said source of potential, meansincluding a condenser for connecting the control electrode of said firstdevice to the negative terminal of said source of potential, and meansincluding a resistance for connecting the control electrode of saidfirst device to the positive terminal of said source of potential.

3. A circuit for producing current and voltage variations of saw-toothwave form comprising a first and a second discharge device eachincluding at least a cathode, a control electrode and an anode, meansincluding a common resistance for connecting said cathodes to thenegative terminal of a source of potential, resistance means forconnecting the control electrode of said second device to said cathodes,means including a condenser for connecting the anode of said firstdevice to the control electrode of said second device, means forconnecting the anode of said second device to said source of potential,means including a resistance for connecting the anode of said firstdevice to said source of potential, and means including a condenser anda resistance for connecting the control electrode of said first deviceto the positive terminal of said source of potential.

4. A circuit for producing current and voltage variations of saw-toothwave form comprising a source of potential, series means connectedacross said source including a first resistor, a condenser and a secondand third resistor, a first and a second discharge device each includingat least a cathode, a control electrode and an anode, means forconnecting said cathodes to the junction of said second and thirdresistors, means for connecting the control electrode of said seconddevice to the junction of said condenser and said second resistor, meansfor connecting the anode of said first device to the junction of saidfirst resistor and said condenser, means for connecting the anode ofsaid second device to the positive terminal of said source of potential,and a resistance and condenser one terminal of each of which isconnected to the control electrode of said first device and the otherterminals being connected to the source of potential.

5. A circuit for producing current and voltage variations of saw-toothwave form comprising a source of potential, series means connectedacross said source including a first resistor, a condenser, a secondresistor, a third resistor, a first and a second discharge device eachincluding at least a cathode, a control electrode and an anode, meansfor connecting said cathodes to the junction of said second and thirdresistor, means for connecting the control electrode of said seconddevice to the junction of said condenser and said second resistor, meansfor connecting the anode of said first device to the junction of saidfirst resistor and said condenser, means for connecting the anode ofsaid second device to the positive terminal of said source of potential,another condenser and resistor connected in series across said source ofcurrent,

and means for connecting the control electrode of said first device tothe junction of said last named condenser and resistor.

6. A circuit for producing current and voltage variations of saw-toothwave form comprising a source of potential, series means connectedacross said source including a first resistor, a condenser, a secondresistor, a third resistor, a first and a second discharge device eachincluding at least a cathode, a control electrode and an anode, meansfor connecting said cathodes to the Junction of said second and thirdresistor,

means for connecting the control electrode of said second device to thejunction of said condenser and said second resistor, means forconnecting the anode of said first device to the junction of said firstresistor and said condenser, means for connecting the anode of saidsecond device to the positive terminal-oi said source of potential, andmeans including a resistor and a condenser for connecting the controlelectrode of said first device to the said source of potential.

ERIC LAWRENCE CASLING WHITE.

positive terminal of 10

